The present invention relates to a screen printing machine of the type utilizing an endless travelling printing screen.
Screen printing machines are either of the type having a flat or planar printing screen, or of the type having an endless travelling printing screen. The latter type comes in two basic varieties, one wherein the printing screen is tubular and the other wherein the printing screen is an endless belt which is trained about a plurality of rollers, usually three rollers which are arranged at the corners of a triangle. In either case, the printing screen is of generally annular configuration.
Screen printing machines of the type having an endless travelling printing screen may be provided with one or more printing stations at each of which one of these printing screens is provided. If two or more such stations are utilized, the machine is suitable for multi-color printing. Usually, the first station (as seen in the direction of workpiece travel), prints the lightest color of the pattern, and succeeding stations print successively darker colors of the pattern. The workpiece web, such as a textile web, a carpet web or the like, is supplied beneath the printing screen, in some instances on a printing blanket which travels beneath the printing screen relative to the same and supports the web. At each printing station a printing medium, for example printing ink, ink paste or the like, is admitted into the interior of the space surrounded by the endless printing screen and is then usually squeezed by means of a squeegee or the like, through the perforations of the printing screen and onto the underlying workpiece web. The perforations of the screen which have been left permeable to the printing medium -- other perforations having been made impermeable -- produce the desired printing pattern.
The disadvantage of the prior-art printing machines is that the pattern is repeated again and again on the workpiece, i.e. the pattern is repeated in a constantly recurring uniform sequence which can be changed only by replacing the printing screen with another printing screen having a different pattern and/or a different repeat.